Margos,
Make it simple and make it easy or it won't happen enough to be valuable to anybody.
I have been a navigator all my life. Log books are a feature of that life. These days, I keep it on a laptop and store it either in a flashdrive or in my DropBox. (Not in the unit HDD - that lesson learned.) I do it in what ever text editor (word processor) I like today and Start each day with departure time, weather and planned destination. My wife drives a lot, so I keep it up during the day's travel and at EOD (End Of Day) I log the time and indicated miles.
These are simple and I frequently pass the file to someone with questions about an area that we have traveled.
Matt